This invention relates to an apparatus for the pneumatic injection of pulverulent materials into a pressurized vessel comprising a storage silo, a distribution silo, a series of metering means for extracting the pulverulent materials from the distribution silo, pneumatic conveying pipes connecting each of the metering means to the vessel, and also means for the automatic transfer of the pulverulent material from the storage silo (which is under substantially atmospheric pressure) to the distribution silo in which a pressure higher than that in the vessel prevails. Although not limited to this application, the present invention will be described with reference to its most advantageous application, namely the injection of solid fuels into a shaft furnace.
An apparatus of the kind described above is known from the patent application EP-A-No. 0 079 444 corresponding to U.S. Pat. No. 4,593,727, which is assigned to the assignee hereof, all of the contents of which are incorporated herein by reference. In the prior apparatus described in U.S. Pat. No. 4,593,727, the pulverulent material is transferred from the storage silo to the distribution silo by way of an intermediate silo serving as a lock chamber. This intermediate silo is connected alternately by means of a set of valves to the storage silo and to the distribution silo; in other words, it is alternately pressurized and vented. In view of the fact that the pulverulent material is continuously extracted from the distribution silo, that is, without interruption, it is necessary for the volume of the intermediate silo to be relatively large in order to enable sufficient material to be transferred to the distribution silo to ensure that there will be no interruption during the filling of the intermediate silo. Similarly, the pipes and valves must be sufficiently wide to reduce the time required for transfer from one silo to the other. Furthermore, in order to permit the venting of the intermediate silo and ensure the security of the distribution silo, these two silos are connected via sets of valves to a vent pipe provided with a filter. However, while suitable for its intended purposes, all of these conditions, requirements and precautionary measures make the installation described in U.S. Pat. No. 4,593,727, relatively complex, cumbersome and consequently relatively expensive.